U.S. patent number 8,283,261 [Application Number 12/124,855] was granted by the patent office on 2012-10-09 for radical oxidation process for fabricating a nonvolatile charge trap memory device.
This patent grant is currently assigned to Cypress Semiconductor Corporation. Invention is credited to Krishnaswamy Ramkumar.
United States Patent |
8,283,261 |
Ramkumar |
October 9, 2012 |
Radical oxidation process for fabricating a nonvolatile charge trap
memory device
Abstract
A method for fabricating a nonvolatile charge trap memory device
is described. The method includes providing a substrate having a
charge-trapping layer disposed Thereon. A portion of the
charge-trapping layer is then oxidized to form a blocking
dielectric layer above the charge-trapping layer by exposing the
charge-trapping layer to a radical oxidation process.
Inventors: |
Ramkumar; Krishnaswamy (San
Jose, CA) |
Assignee: |
Cypress Semiconductor
Corporation (San Jose, CA)
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Family
ID: |
40072822 |
Appl.
No.: |
12/124,855 |
Filed: |
May 21, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080293255 A1 |
Nov 27, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60940139 |
May 25, 2007 |
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60986637 |
Nov 9, 2007 |
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Current U.S.
Class: |
438/758; 438/769;
438/770; 257/E21.24; 438/786; 438/257; 438/774 |
Current CPC
Class: |
H01L
21/3144 (20130101); H01L 21/3145 (20130101); H01L
29/4234 (20130101); H01L 29/40117 (20190801); H01L
29/66833 (20130101) |
Current International
Class: |
H01L
21/31 (20060101) |
Field of
Search: |
;438/758,769-774,786,954,257,261 ;257/E21.24 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
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USPTO Non-Final Rejection for U.S. Appl. No. 10/185,470 dated Oct.
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09/920,378 dated Jul. 22, 2002; 4 pages. cited by other .
Milton Ohring, "The Materials Science of Thin Films: Deposition and
Structure," 2nd Edition, Academic Press, 2002, pp. 336-337; 4
pages. cited by other .
U.S. Appl. No. 12/197,466 "Radical Oxidation Process for
Fabricating a Nonvolatile Charge Trap Memory Device," Ramkumar et
al., filed on Aug. 25, 2008; 68 pages. cited by other .
USPTO Requirement Restriction for U.S. Appl. No. 12/197,466 dated
Mar. 11, 2011; 5 pages. cited by other .
USPTO Non-Final Rejection for U.S. Appl. No. 12/197,466 dated Jun.
1, 2011; 11 pages. cited by other .
U.S. Appl. No. 13/539,458: "Radical Oxidation Process for
Fabricating a Nonvolatile Charge Trap Memory Device", filed on Jul.
1, 2012; 96 pages. cited by other .
Application No. 60/940,139 "Radical Oxidation for In-Situ ONO
Deposition" filed May 25, 2007 ; 3 pages. cited by other .
Application No. 60/986,637 "Single Wafer Radical Oxidation for ONO
Stack With Bilayer Oxynitride"; filed Nov. 9, 2007; 1 page. cited
by other .
Chinese Office Action for Application No. 20080000820.3 dated Jan.
26, 2011; 6 pages. cited by other .
International Search Report and Written Opinion for Application No.
PCT/US08/06627 dated Aug. 26, 2008; 3 pages. cited by other .
USPTO Advisory Action for U.S. Appl. No. 12/197,466 dated Jan. 31,
2012; 3 pages. cited by other .
USPTO Final Rejection for U.S. Appl. No. 12/197,466 dated Nov. 17,
2011; 13 pages. cited by other .
USPTO Notice of Allowance for U.S. Appl. No. 12/197,466 dated Jun.
15, 2012; 4 pages. cited by other.
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Primary Examiner: Nguyen; Thanh
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
No. 60/940,139, filed May 25, 2007, and U.S. Provisional
Application No. 60/986,637, filed Nov. 9, 2007, the entire contents
of which are hereby incorporated by reference herein.
Claims
What is claimed is:
1. A method of fabricating a nonvolatile charge trap memory device,
the method comprising: oxidizing a portion of a charge-trapping
layer disposed above a substrate to form a blocking dielectric
layer above the charge-trapping layer, the oxidizing performed by
exposing the charge-trapping layer to a hydrogen and oxygen radical
oxidation process, wherein the charge-trapping layer comprises a
bottom oxygen-rich silicon oxy-nitride portion having a thickness
approximately in the range of 2.5-3.5 nanometers and a top
silicon-rich silicon oxy-nitride portion having a thickness
approximately in the range of 9-10 nanometers, and wherein
oxidizing the portion of the charge-trapping layer comprises
oxidizing the top approximately 2 nanometers to approximately 3
nanometers of the top silicon-rich silicon oxy-nitride portion to
form the blocking dielectric layer having a thickness approximately
in the range of 3.5-4.5 nanometers.
2. A method of fabricating a nonvolatile charge trap memory device,
comprising: subjecting, in a process chamber, a substrate to a
first hydrogen and oxygen radical oxidation process to form a first
dielectric layer; subjecting, in the process chamber, the substrate
to a deposition process to form a charge-trapping layer above the
first dielectric layer; and subjecting, in the process chamber, the
substrate to a second hydrogen and oxygen radical oxidation process
to form a second dielectric layer above the charge-trapping layer
by oxidizing a portion of the charge-trapping layer, wherein the
charge-trapping layer comprises a bottom oxygen-rich silicon
oxy-nitride portion having a thickness approximately in the range
of 2.5-3.5 nanometers and a top silicon-rich silicon oxy-nitride
portion having a thickness approximately in the range of 9-10
nanometers, and wherein oxidizing the portion of the
charge-trapping layer comprises oxidizing the top approximately 2
nanometers to approximately 3 nanometers of the top silicon-rich
silicon oxy-nitride portion to form the second dielectric layer
having a thickness approximately in the range of 3.5-4.5
nanometers.
3. A method of fabricating a nonvolatile charge trap memory device,
comprising: subjecting a substrate to an oxidation process to form
a first dielectric layer; depositing a charge-trapping layer above
the first dielectric layer, the charge-trapping layer comprising a
bottom portion and a top portion; and subjecting the
charge-trapping layer to a radical oxidation process to form a
second dielectric layer above the charge-trapping layer by exposing
the charge-trapping layer to a hydrogen (H.sub.2) and oxygen
(O.sub.2) gas flow, forming radicals at a surface of the
charge-trapping layer, and consuming a portion of the top portion
of the charge-trapping layer to form the second dielectric layer,
wherein the bottom portion of the charge-trapping layer comprises
an oxygen-rich silicon oxy-nitride.
4. The method of claim 3, wherein the radical oxidation process
does not include an ignition event to pyrolyze the H.sub.2 and
O.sub.2 gas to form steam.
5. The method of claim 3, wherein the oxidation process to form the
first dielectric layer is also a radical oxidation process
comprising exposing the substrate to a H.sub.2 and O.sub.2 gas
flow, and forming radicals at a surface of the substrate to form
the second dielectric layer.
6. The method of claim 3, further comprising subjecting the second
dielectric layer to a nitridation process by annealing the
substrate in a nitrogen containing atmosphere.
Description
TECHNICAL FIELD
Embodiments of the present invention are in the field of
Semiconductor Fabrication and, in particular, Semiconductor Device
Fabrication.
BACKGROUND
For the past several decades, the scaling of features in integrated
circuits has been a driving force behind an ever-growing
semiconductor industry. Scaling to smaller and smaller features
enables increased densities of functional units on the limited real
estate of semiconductor chips. For example, shrinking transistor
size allows for the incorporation of an increased number of memory
devices on a chip, lending to the fabrication of products with
increased capacity. The drive for ever-more capacity, however, is
not without issue. The necessity to optimize the performance of
each device becomes increasingly significant.
Non-volatile semiconductor memories typically use stacked floating
gate type field-effect-transistors. In such transistors, electrons
are injected into a floating gate of a memory cell to be programmed
by biasing a control gate and grounding a body region of a
substrate on which the memory cell is formed. An
oxide-nitride-oxide (ONO) stack is used as either a charge storing
layer, as in a semiconductor-oxide-nitride-oxide-semiconductor
(SONOS) transistor, or as an isolation layer between the floating
gate and control gate, as in a split gate flash transistor. FIG. 1
illustrates a cross-sectional view of a conventional nonvolatile
charge trap memory device.
Referring to FIG. 1, semiconductor device 100 includes a SONOS gate
stack 104 including a conventional ONO portion 106 formed over a
silicon substrate 102. Semiconductor device 100 further includes
source and drain regions 110 on either side of SONOS gate stack 104
to define a channel region 112. SONOS gate stack 104 includes a
poly-silicon gate layer 108 formed above and in contact with ONO
portion 106. Poly-silicon gate layer 108 is electrically isolated
from silicon substrate 102 by ONO portion 106. ONO portion 106
typically includes a tunnel oxide layer 106A, a nitride or
oxy-nitride charge-trapping layer 106B, and a top oxide layer 106C
overlying nitride or oxy-nitride layer 106B.
One problem with conventional SONOS transistors is the poor data
retention in the nitride or oxy-nitride layer 106B that limits
semiconductor device 100 lifetime and its use in several
applications due to leakage current through the layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cross-sectional view of a conventional
nonvolatile charge trap memory device.
FIG. 2 illustrates a cross-sectional view of an oxidation chamber
of a batch-processing tool, in accordance with an embodiment of the
present invention.
FIG. 3 depicts a Flowchart representing a series of operations in a
method for fabricating a nonvolatile charge trap memory device, in
accordance with an embodiment of the present invention.
FIG. 4A illustrates a cross-sectional view of a substrate having a
charge-trapping layer formed thereon, corresponding to operation
302 from the Flowchart of FIG. 3, in accordance with an embodiment
of the present invention.
FIG. 4B illustrates a cross-sectional view of a substrate having a
charge-trapping layer with a blocking dielectric layer formed
thereon, corresponding to operation 304 from the Flowchart of FIG.
3, in accordance with an embodiment of the present invention.
FIG. 5 depicts a Flowchart representing a series of operations in a
method for fabricating a nonvolatile charge trap memory device, in
accordance with an embodiment of the present invention.
FIG. 6A illustrates a cross-sectional view of a substrate,
corresponding to operation 502 from the Flowchart of FIG. 5, in
accordance with an embodiment of the present invention.
FIG. 6B illustrates a cross-sectional view of a substrate having a
first dielectric layer formed thereon, corresponding to operation
504 from the Flowchart of FIG. 5, in accordance with an embodiment
of the present invention.
FIG. 6C illustrates a cross-sectional view of a substrate having a
charge-trapping layer formed thereon, corresponding to operation
508 from the Flowchart of FIG. 5, in accordance with an embodiment
of the present invention.
FIG. 6D illustrates a cross-sectional view of a substrate having a
charge-trapping layer with a blocking dielectric layer formed
thereon, corresponding to operation 510 from the Flowchart of FIG.
5, in accordance with an embodiment of the present invention.
FIG. 6E illustrates a cross-sectional view of a nonvolatile charge
trap memory device, in accordance with an embodiment of the present
invention.
FIG. 7A illustrates a cross-sectional view of a substrate including
first and second exposed crystal planes, in accordance with an
embodiment of the present invention.
FIG. 7B illustrates a cross-sectional view of the substrate
including first and second crystal planes and having a dielectric
layer formed thereon, in accordance with an embodiment of the
present invention.
FIG. 8 illustrates an arrangement of process chambers in a cluster
tool, in accordance with an embodiment of the present
invention.
FIG. 9 depicts a Flowchart representing a series of operations in a
method for fabricating a nonvolatile charge trap memory device, in
accordance with an embodiment of the present invention.
FIG. 10A illustrates a cross-sectional view of a substrate, in
accordance with an embodiment of the present invention.
FIG. 10B illustrates a cross-sectional view of a substrate having a
tunnel dielectric layer formed thereon, corresponding to operation
402 from the Flowchart of FIG. 4, in accordance with an embodiment
of the present invention.
FIG. 10C illustrates a cross-sectional view of a substrate having a
charge-trapping layer formed thereon, corresponding to operation
406 from the Flowchart of FIG. 4, in accordance with an embodiment
of the present invention.
FIG. 10D illustrates a cross-sectional view of a substrate having a
top dielectric layer formed thereon, corresponding to operation 408
from the Flowchart of FIG. 4, in accordance with an embodiment of
the present invention.
FIG. 10E illustrates a cross-sectional view of a nonvolatile charge
trap memory device, in accordance with an embodiment of the present
invention.
FIG. 11 depicts a Flowchart representing a series of operations in
a method for fabricating a nonvolatile charge trap memory device,
in accordance with an embodiment of the present invention.
FIG. 12A illustrates a cross-sectional view of a substrate having a
tunnel dielectric layer formed thereon, corresponding to operation
602 from the Flowchart of FIG. 6, in accordance with an embodiment
of the present invention.
FIG. 12B illustrates a cross-sectional view of a substrate having
an oxygen-rich silicon oxy-nitride portion of a charge-trapping
layer formed thereon, corresponding to operation 606 from the
Flowchart of FIG. 6, in accordance with an embodiment of the
present invention.
FIG. 12C illustrates a cross-sectional view of a substrate having a
silicon-rich silicon oxy-nitride portion of a charge-trapping layer
formed thereon, corresponding to the operation 610 from the
Flowchart of FIG. 6, in accordance with an embodiment of the
present invention.
FIG. 12D illustrates a cross-sectional view of a substrate having a
top dielectric layer formed thereon, corresponding to operation 612
from the Flowchart of FIG. 6, in accordance with an embodiment of
the present invention.
FIG. 12E illustrates a cross-sectional view of a nonvolatile charge
trap memory device, in accordance with an embodiment of the present
invention.
FIG. 13A illustrates a cross-sectional view of a substrate
including first and second exposed crystal planes, in accordance
with an embodiment of the present invention.
FIG. 13B illustrates a cross-sectional view of the substrate
including first and second crystal planes and having a dielectric
layer formed thereon, in accordance with an embodiment of the
present invention.
DETAILED DESCRIPTION
Methods to fabricate a nonvolatile charge trap memory device are
described herein. In the following description, numerous specific
details are set forth, such as specific dimensions, in order to
provide a thorough understanding of the present invention. It will
be apparent to one skilled in the art that the present invention
may be practiced without these specific details. In other
instances, well-known processing steps, such as patterning steps or
wet chemical cleans, are not described in detail in order to not
unnecessarily obscure the present invention. Furthermore, it is to
be understood that the various embodiments shown in the Figures are
illustrative representations and are not necessarily drawn to
scale.
Disclosed herein is a method to fabricate a nonvolatile charge trap
memory device. A substrate may first be provided having a
charge-trapping layer disposed thereon. In one embodiment, a
portion of the charge-trapping layer is then oxidized to form a
blocking dielectric layer above the charge-trapping layer by
exposing the charge-trapping layer to a radical oxidation
process.
Formation of a dielectric layer by a radical oxidation process may
provide higher quality films than processes involving steam growth,
i.e. wet growth processes. Furthermore, a radical oxidation process
carried out in a batch-processing chamber may provide high quality
films without impacting the throughput (wafers/Hr) requirements
that a fabrication facility may require. By carrying out the
radical oxidation process at temperatures compatible with such a
chamber, such as temperatures approximately in the range of 600-900
degrees Celsius, the thermal budget tolerated by the substrate and
any other features on the substrate may not be impacted to the
extent typical of processes over 1000 degrees Celsius. In
accordance with an embodiment of the present invention, a radical
oxidation process involving flowing hydrogen (H.sub.2) and oxygen
(O.sub.2) gas into a batch-processing chamber is carried out to
effect growth of a dielectric layer by oxidation consumption of an
exposed substrate or film. In one embodiment, multiple radical
oxidation processes are carried out to provide a tunnel dielectric
layer and a blocking dielectric layer for a non-volatile charge
trap memory device. These dielectric layers may be of very high
quality, even at a reduced thickness. In one embodiment, the tunnel
dielectric layer and the blocking dielectric layer are both denser
and are composed of substantially fewer hydrogen atoms/cm.sup.3
than a tunnel dielectric layer or a blocking dielectric layer
formed by wet oxidation techniques. In accordance with another
embodiment of the present invention, a dielectric layer formed by
carrying out a radical oxidation process is less susceptible to
crystal plane orientation differences in the substrate from which
it is grown. In one embodiment, the cornering effect caused by
differential crystal plane oxidation rates is significantly reduced
by forming a dielectric layer via a radical oxidation process.
A portion of a nonvolatile charge trap memory device may be
fabricated by carrying out a radical oxidation process in a process
chamber. In accordance with an embodiment of the present invention,
the process chamber is a batch-processing chamber. FIG. 2
illustrates a cross-sectional view of an oxidation chamber of a
batch-processing tool, in accordance with that embodiment.
Referring to FIG. 2, a batch-processing chamber 200 includes a
carrier apparatus 204 to hold a plurality of semiconductor wafers
202. In one embodiment, the batch-processing chamber is an
oxidation chamber. In a specific embodiment, the process chamber is
a low-pressure chemical vapor deposition chamber. The plurality of
semiconductor wafers 202 may be arranged in such a way as to
maximize exposure of each wafer to a radical oxidation process,
while enabling the inclusion of a reasonable number of wafers (e.g.
25 wafers), to be processed in a single pass. It should be
understood, however, that the present invention is not limited to a
batch-processing chamber.
In an aspect of the present invention, a portion of a nonvolatile
charge trap memory device is fabricated by a radical oxidation
process. FIG. 3 depicts a Flowchart representing a series of
operations in a method for fabricating a nonvolatile charge trap
memory device, in accordance with an embodiment of the present
invention. FIGS. 4A-4B illustrate cross-sectional views
representing operations in the fabrication of a nonvolatile charge
trap memory device, in accordance with an embodiment of the present
invention.
FIG. 4A illustrates a cross-sectional view of a substrate having a
charge-trapping layer formed thereon, corresponding to operation
302 from the Flowchart of FIG. 3, in accordance with an embodiment
of the present invention. Referring to operation 302 of Flowchart
300 and corresponding FIG. 4A, a substrate 400 is provided having a
charge-trapping layer disposed thereon. In an embodiment, the
charge-trapping layer has a first region 404A and a second region
404B disposed above substrate 400. In one embodiment, a dielectric
layer 402 is disposed between substrate 400 and the charge-trapping
layer, as depicted in FIG. 4A. The charge-trapping layer may be
composed of a material and have a thickness suitable to store
charge and, hence, change the threshold voltage of a subsequently
formed gate stack. In an embodiment, region 404A of the
charge-trapping layer will remain as an intact charge-trapping
layer following subsequent process operations. However, in that
embodiment, region 404B of the as-formed charge-trapping layer will
be consumed to form a second dielectric layer, above region
404A.
FIG. 4B illustrates a cross-sectional view of a substrate having a
charge-trapping layer with a blocking dielectric layer formed
thereon, corresponding to operation 304 from the Flowchart of FIG.
3, in accordance with an embodiment of the present invention.
Referring to operation 304 of Flowchart 300 and corresponding FIG.
4B, a blocking dielectric layer 406 is formed on charge-trapping
layer 404. In accordance with an embodiment of the present
invention, blocking dielectric layer 406 is formed by oxidizing
region 404B of the charge-trapping layer by exposing the
charge-trapping layer to a radical oxidation process. In that
embodiment, region 404A of the original charge-trapping layer is
now labeled as charge-trapping layer 404.
Blocking dielectric layer 406 may be composed of a material and
have a thickness suitable to maintain a barrier to charge leakage
without significantly decreasing the capacitance of a subsequently
formed gate stack in a nonvolatile charge trap memory device. In a
specific embodiment, region 404B is a silicon-rich silicon
oxy-nitride region having a thickness approximately in the range of
2-3 nanometers and is oxidized to form blocking dielectric layer
406 having a thickness approximately in the range of 3.5-4.5
nanometers. In that embodiment, blocking dielectric layer 406 is
composed of silicon dioxide.
Blocking dielectric layer 406 may be formed by a radical oxidation
process. In accordance with an embodiment of the present invention,
the radical oxidation process involves flowing hydrogen (H.sub.2)
and oxygen (O.sub.2) gas into a furnace, such as the batch
processing chamber 200 described in association with FIG. 2. In one
embodiment, the partial pressures of H.sub.2 and O.sub.2 have a
ratio to one another of approximately 1:1. However, in an
embodiment, an ignition event is not carried out which would
otherwise typically be used to pyrolyze the H.sub.2 and O.sub.2 to
form steam. Instead, H.sub.2 and O.sub.2 are permitted to react to
form radicals at the surface of region 404B. In one embodiment, the
radicals are used to consume region 404B to provide blocking
dielectric layer 406. In a specific embodiment, the radical
oxidation process includes oxidizing with a radical such as, but
not limited to, an OH radical, an HO.sub.2 radical or an O
diradical at a temperature approximately in the range of 600-900
degrees Celsius. In a particular embodiment, the radical oxidation
process is carried out at a temperature approximately in the range
of 700-800 degrees Celsius at a pressure approximately in the range
of 0.5-5 Torr. In one embodiment, the second radical oxidation
process is carried out for a duration approximately in the range of
100-150 minutes.
Referring to operation 306 of Flowchart 300, blocking dielectric
layer 406 may be further subjected to a nitridation process in the
first process chamber. In accordance with an embodiment of the
present invention, the nitridation process includes annealing
blocking dielectric layer 406 in an atmosphere including nitrogen
at a temperature approximately in the range of 700-800 degrees
Celsius for a duration approximately in the range of 5 minutes-60
minutes. In one embodiment, the atmosphere including nitrogen is
composed of a gas such as, but not limited to, nitrogen (N.sub.2),
nitrous oxide (N.sub.2O), nitrogen dioxide (NO.sub.2), nitric oxide
(NO) or ammonia (NH.sub.3). Alternatively, this nitridation step,
i.e. operation 306 from Flowchart 300, may be skipped.
In an aspect of the present invention, both a tunnel dielectric
layer and a blocking dielectric layer may be formed by radical
oxidation processes. FIG. 5 depicts a Flowchart 500 representing a
series of operations in a method for fabricating a nonvolatile
charge trap memory device, in accordance with an embodiment of the
present invention. FIGS. 6A-6E illustrate cross-sectional views
representing operations in the fabrication of a nonvolatile charge
trap memory device, in accordance with an embodiment of the present
invention.
FIG. 6A illustrates a cross-sectional view of a substrate,
corresponding to operation 502 from the Flowchart of FIG. 5, in
accordance with an embodiment of the present invention. Referring
to operation 502 of Flowchart 500 and corresponding FIG. 6A, a
substrate 600 is provided in a process chamber.
Substrate 600 may be composed of a material suitable for
semiconductor device fabrication. In one embodiment, substrate 600
is a bulk substrate composed of a single crystal of a material
which may include, but is not limited to, silicon, germanium,
silicon-germanium or a III-V compound semiconductor material. In
another embodiment, substrate 600 includes a bulk layer with a top
epitaxial layer. In a specific embodiment, the bulk layer is
composed of a single crystal of a material which may include, but
is not limited to, silicon, germanium, silicon-germanium, a III-V
compound semiconductor material or quartz, while the top epitaxial
layer is composed of a single crystal layer which may include, but
is not limited to, silicon, germanium, silicon-germanium or a III-V
compound semiconductor material. In another embodiment, substrate
600 includes a top epitaxial layer on a middle insulator layer
which is above a lower bulk layer. The top epitaxial layer is
composed of a single crystal layer which may include, but is not
limited to, silicon (i.e. to form a silicon-on-insulator (SOI)
semiconductor substrate), germanium, silicon-germanium or a III-V
compound semiconductor material. The insulator layer is composed of
a material which may include, but is not limited to, silicon
dioxide, silicon nitride or silicon oxy-nitride. The lower bulk
layer is composed of a single crystal which may include, but is not
limited to, silicon, germanium, silicon-germanium, a III-V compound
semiconductor material or quartz. Substrate 600 may further include
dopant impurity atoms.
FIG. 6B illustrates a cross-sectional view of a substrate having a
dielectric layer formed thereon, corresponding to operation 504
from the Flowchart of FIG. 5, in accordance with an embodiment of
the present invention. Referring to operation 504 of Flowchart 500
and corresponding FIG. 6B, substrate 600 is subjected to a first
radical oxidation process to form a first dielectric layer 602.
First dielectric layer 602 may be composed of a material and have a
thickness suitable to allow charge carriers to tunnel into a
subsequently formed charge-trapping layer under an applied gate
bias, while maintaining a suitable barrier to leakage when a
subsequently formed nonvolatile charge trap memory device is
unbiased. First dielectric layer 602 may be referred to in the art
as a tunnel dielectric layer. In accordance with an embodiment of
the present invention, first dielectric layer 602 is formed by an
oxidation process where the top surface of substrate 600 is
consumed. Thus, in an embodiment, first dielectric layer 602 is
composed of an oxide of the material of substrate 600. For example,
in one embodiment, substrate 600 is composed of silicon and first
dielectric layer 602 is composed of silicon dioxide. In a specific
embodiment, first dielectric layer 602 is formed to a thickness
approximately in the range of 1-10 nanometers. In a particular
embodiment, first dielectric layer 602 is formed to a thickness
approximately in the range of 1.5-2.5 nanometers.
First dielectric layer 602 may be formed by a radical oxidation
process. In accordance with an embodiment of the present invention,
the radical oxidation process involves flowing hydrogen (H.sub.2)
and oxygen (O.sub.2) gas into a furnace, such as the batch
processing chamber 200 described in association with FIG. 2. In one
embodiment, the partial pressures of H.sub.2 and O.sub.2 have a
ratio to one another of approximately 1:1. However, in an
embodiment, an ignition event is not carried out which would
otherwise typically be used to pyrolyze the H.sub.2 and O.sub.2 to
form steam. Instead, H.sub.2 and O.sub.2 are permitted to react to
form radicals at the surface of substrate 600. In one embodiment,
the radicals are used to consume the top portion of substrate 600
to provide first dielectric layer 602. In a specific embodiment,
the radical oxidation process includes oxidizing with a radical
such as, but not limited to, an OH radical, an HO.sub.2 radical or
an O diradical at a temperature approximately in the range of
600-900 degrees Celsius. In a particular embodiment, the radical
oxidation process is carried out at a temperature approximately in
the range of 700-800 degrees Celsius at a pressure approximately in
the range of 0.5-5 Torr. In one embodiment, the radical oxidation
process is carried out for a duration approximately in the range of
100-150 minutes. In accordance with an embodiment of the present
invention, first dielectric layer 602 is formed as a high-density,
low-hydrogen-content film.
Referring to operation 506 of Flowchart 500, subsequent to forming
first dielectric layer 602, but prior to any further processing,
first dielectric layer 602 may be subjected to a nitridation
process. In an embodiment, the nitridation process is carried out
in the same process chamber used to form first dielectric layer
502, without removing substrate 600 from the process chamber
between process steps. In one embodiment, the annealing includes
heating substrate 600 in an atmosphere including nitrogen at a
temperature approximately in the range of 700-800 degrees Celsius
for a duration approximately in the range of 5 minutes-60 minutes.
In one embodiment, the atmosphere including nitrogen is composed of
a gas such as, but not limited to, nitrogen (N.sub.2), nitrous
oxide (N.sub.2O), nitrogen dioxide (NO.sub.2), nitric oxide (NO) or
ammonia (NH.sub.3). In one embodiment, the nitridation occurs
following a nitrogen or argon purge of the process chamber
following the first radical oxidation process. Alternatively, the
above nitridation step may be skipped.
FIG. 6C illustrates a cross-sectional view of a substrate having a
charge-trapping layer formed thereon, corresponding to operation
508 from the Flowchart of FIG. 5, in accordance with an embodiment
of the present invention. Referring to operation 508 of Flowchart
500 and corresponding FIG. 6C, a charge-trapping layer having a
first region 604A and a second region 604B is formed on first
dielectric layer 602. In an embodiment, the formation of the
charge-trapping layer is carried out in the same process chamber
used to form first dielectric layer 602, without removing substrate
600 from the process chamber between process steps.
The charge-trapping layer may be composed of a material and have a
thickness suitable to store charge and, hence, change the threshold
voltage of a subsequently formed gate stack. In accordance with an
embodiment of the present invention, the charge-trapping layer is
composed of two regions 604A and 604B, as depicted in FIG. 6C. In
an embodiment, region 604A of the charge-trapping layer will remain
as an intact charge-trapping layer following subsequent process
operations. However, in that embodiment, region 604B of the
as-formed charge-trapping layer will be consumed to form a second
dielectric layer, above region 604A.
The charge-trapping layer having regions 604A and 604B may be
formed by a chemical vapor deposition process. In accordance with
an embodiment of the present invention, the charge-trapping layer
is composed of a material such as, but not limited to, silicon
nitride, silicon oxy-nitride, oxygen-rich silicon oxy-nitride or
silicon-rich silicon oxy-nitride. In one embodiment, regions 604A
and 604B of the charge-trapping layer are formed at a temperature
approximately in the range of 600-900 degrees Celsius. In a
specific embodiment, the charge-trapping layer is formed by using
gases such as, but not limited to, dichlorosilane
(H.sub.2SiCl.sub.2), bis-(tert-butylamino)silane (BTBAS), ammonia
(NH.sub.3) or nitrous oxide (N.sub.2O). In one embodiment, the
charge-trapping layer is formed to a total thickness approximately
in the range of 5-15 nanometers and region 604B accounts for a
thickness approximately in the range of 2-3 nanometers of the total
thickness of the charge-trapping layer. In that embodiment, region
604A accounts for the remaining total thickness of the
charge-trapping layer, i.e. region 604A accounts for the portion of
the charge-trapping layer that is not subsequently consumed to form
a top or blocking dielectric layer.
In another aspect of the present invention, the charge-trapping
layer may include multiple composition regions. For example, in
accordance with an embodiment of the present invention, the
charge-trapping layer includes an oxygen-rich portion and a
silicon-rich portion and is formed by depositing an oxygen-rich
oxy-nitride film by a first composition of gases and, subsequently,
depositing a silicon-rich oxy-nitride film by a second composition
of gases. In one embodiment, the charge-trapping layer is formed by
modifying the flow rate of ammonia (NH.sub.3) gas, and introducing
nitrous oxide (N.sub.2O) and dichlorosilane (SiH.sub.2Cl.sub.2) to
provide the desired gas ratios to yield first an oxygen-rich
oxy-nitride film and then a silicon-rich oxy-nitride film. In a
specific embodiment, the oxygen-rich oxy-nitride film is formed by
introducing a process gas mixture including N.sub.2O, NH.sub.3 and
SiH.sub.2Cl.sub.2, while maintaining the process chamber at a
pressure approximately in the range of 5-500 mTorr, and maintaining
substrate 600 at a temperature approximately in the range of
700-850 degrees Celsius, for a period approximately in the range of
2.5-20 minutes. In a further embodiment, the process gas mixture
includes N.sub.2O and NH.sub.3 having a ratio of from about 8:1 to
about 1:8 and SiH.sub.2Cl.sub.2 and NH.sub.3 having a ratio of from
about 1:7 to about 7:1, and can be introduced at a flow rate
approximately in the range of 5-200 standard cubic centimeters per
minute (sccm). In another specific embodiment, the silicon-rich
oxy-nitride film is formed by introducing a process gas mixture
including N.sub.2O, NH.sub.3 and SiH.sub.2Cl.sub.2, while
maintaining the chamber at a pressure approximately in the range of
5-500 mTorr, and maintaining substrate 600 at a temperature
approximately in the range of 700-850 degrees Celsius, for a period
approximately in the range of 2.5-20 minutes. In a further
embodiment, the process gas mixture includes N.sub.2O and NH.sub.3
having a ratio of from about 8:1 to about 1:8 and SiH.sub.2Cl.sub.2
and NH.sub.3 mixed in a ratio of from about 1:7 to about 7:1,
introduced at a flow rate of from about 5 to about 20 sccm. In
accordance with an embodiment of the present invention, the
charge-trapping layer comprises a bottom oxygen-rich silicon
oxy-nitride portion having a thickness approximately in the range
of 2.5-3.5 nanometers and a top silicon-rich silicon oxy-nitride
portion having a thickness approximately in the range of
9-10nanometers. In one embodiment, a region 504B of charge-trapping
layer accounts for a thickness approximately in the range of 2-3
nanometers of the total thickness of the top silicon-rich silicon
oxy-nitride portion of the charge-trapping layer. Thus, region
604B, which is targeted for subsequent consumption to form a second
dielectric layer, may be composed entirely of silicon-rich silicon
oxy-nitride.
FIG. 6D illustrates a cross-sectional view of a substrate having a
second dielectric layer formed thereon, corresponding to operation
510 from the Flowchart of FIG. 5, in accordance with an embodiment
of the present invention. Referring to operation 510 of Flowchart
500 and corresponding FIG. 6D, a second dielectric layer 606 is
formed on charge-trapping layer 604. In an embodiment, the
formation of second dielectric layer 606 is carried out in the same
process chamber used to form first dielectric layer 602 and the
charge-trapping layer, without removing substrate 600 from the
process chamber between process steps. In one embodiment, the
second radical oxidation process is carried out following a
nitrogen or argon purge of the process chamber following the
deposition of the charge-trapping layer.
Second dielectric layer 606 may be composed of a material and have
a thickness suitable to maintain a barrier to charge leakage
without significantly decreasing the capacitance of a subsequently
formed gate stack in a nonvolatile charge trap memory device.
Second dielectric layer 606 may be referred to in the art as a
blocking dielectric layer or a top dielectric layer. In accordance
with an embodiment of the present invention, second dielectric
layer 606 is formed by consuming region 604B of the charge-trapping
layer formed in operation 508, described in association with FIG.
6C. Thus, in one embodiment, region 604B is consumed to provide
second dielectric layer 606, while region 604A remains a
charge-trapping layer 604. In a specific embodiment, region 604B is
a silicon-rich silicon oxy-nitride region having a thickness
approximately in the range of 2-3 nanometers and is oxidized to
form second dielectric layer 606 having a thickness approximately
in the range of 3.5-4.5 nanometers. In that embodiment, second
dielectric layer 606 is composed of silicon dioxide. In accordance
with an embodiment of the present invention, second dielectric
layer 606 is formed by a second radical oxidation process, similar
to the radical oxidation process carried out to form blocking
dielectric layer 406, described in association with FIG. 4B. In one
embodiment, referring to operation 512 of Flowchart 500, subsequent
to forming second dielectric layer 606, second dielectric layer 606
is further subjected to a nitridation process similar to the
nitridation process described in association with operation 506
from Flowchart 500. In a specific embodiment, the nitridation
occurs following a nitrogen or argon purge of the process chamber
following the second radical oxidation process. Alternatively, this
nitridation step may be skipped. In accordance with an embodiment
of the present invention, no additional deposition processes are
used in the formation of second dielectric layer 606.
Thus, in accordance with an embodiment of the present invention, an
ONO stack including first dielectric layer 602, charge-trapping
layer 604 and second dielectric layer 606 is formed in a single
pass in a process chamber. By fabricating these layers in a single
pass of multiple wafers in the process chamber, high throughput
requirements may be met while still ensuring the formation of very
high quality films. Upon fabrication of an ONO stack including
first dielectric layer 602, charge-trapping layer 604 and second
dielectric layer 606, a nonvolatile charge trap memory device may
be fabricated to include a patterned portion of the ONO stack. FIG.
6E illustrates a cross-sectional view of a nonvolatile charge trap
memory device, in accordance with an embodiment of the present
invention.
Referring to FIG. 6E, a nonvolatile charge trap memory device
includes a patterned portion of the ONO stack formed over substrate
600. The ONO stack includes first dielectric layer 602,
charge-trapping layer 604 and second dielectric layer 606. A gate
layer 608 is disposed on second dielectric layer 606. The
nonvolatile charge trap memory device further includes source and
drain regions 612 in substrate 600 on either side of the ONO stack,
defining a channel region 614 in substrate 600 underneath the ONO
stack. A pair of dielectric spacers 610 isolates the sidewalls of
first dielectric layer 602, charge-trapping layer 604, second
dielectric layer 606 and gate layer 608. In a specific embodiment,
channel region 614 is doped P-type and, in an alternative
embodiment, channel region 614 is doped N-type.
In accordance with an embodiment of the present invention, the
nonvolatile charge trap memory device described in association with
FIG. 6E is a SONOS-type device. By convention, SONOS stands for
"Semiconductor-Oxide-Nitride -Oxide-Semiconductor," where the first
"Semiconductor" refers to the channel region material, the first
"Oxide" refers to the tunnel dielectric layer, "Nitride" refers to
the charge-trapping dielectric layer, the second "Oxide" refers to
the top dielectric layer (also known as a blocking dielectric
layer) and the second "Semiconductor" refers to the gate layer.
Thus, in accordance with an embodiment of the present invention,
first dielectric layer 602 is a tunnel dielectric layer and second
dielectric layer 606 is a blocking dielectric layer.
Gate layer 608 may be composed of any conductor or semiconductor
material suitable for accommodating a bias during operation of a
SONOS-type transistor. In accordance with an embodiment of the
present invention, gate layer 608 is formed by a chemical vapor
deposition process and is composed of doped poly-crystalline
silicon. In another embodiment, gate layer 608 is formed by
physical vapor deposition and is composed of a metal-containing
material which may include, but is not limited to, metal nitrides,
metal carbides, metal silicides, hafnium, zirconium, titanium,
tantalum, aluminum, ruthenium, palladium, platinum, cobalt or
nickel.
Source and drain regions 612 in substrate 600 may be any regions
having opposite conductivity to channel region 614. For example, in
accordance with an embodiment of the present invention, source and
drain regions 612 are N-type doped regions while channel region 614
is a P-type doped region. In one embodiment, substrate 600 and,
hence, channel region 614, is composed of boron-doped
single-crystal silicon having a boron concentration in the range of
1.times.10.sup.15-1.times.10.sup.19 atoms/cm.sup.3. In that
embodiment, source and drain regions 612 are composed of
phosphorous- or arsenic-doped regions having a concentration of
N-type dopants in the range of 5.times.10.sup.16-5.times.10.sup.19
atoms/cm.sup.3. In a specific embodiment, source and drain regions
612 have a depth in substrate 600 in the range of 80-200
nanometers. In accordance with an alternative embodiment of the
present invention, source and drain regions 612 are P-type doped
regions while channel region 614 is an N-type doped region.
In another aspect of the present invention, a dielectric layer
formed by radical oxidation of the top surface of a substrate in an
oxidation chamber may be less susceptible to crystal plane
orientation differences in the substrate upon which it is grown.
For example, in one embodiment, the cornering effect caused by
differential crystal plane oxidation rates is significantly reduced
by forming a dielectric layer by a radical oxidation process. FIG.
7A illustrates a cross-sectional view of a substrate including
first and second exposed crystal planes, in accordance with an
embodiment of the present invention.
Referring to FIG. 7A, a substrate 700 has isolation regions 702
formed thereon. Substrate 700 may be composed of a material
described in association with substrate 600 from FIG. 6A. Isolation
regions 702 may be composed of an insulating material suitable for
adhesion to substrate 700. An exposed portion of substrate 700
extends above the top surface of isolation regions 702. In
accordance with an embodiment of the present invention, the exposed
portion of substrate 700 has a first exposed crystal plane 704 and
a second exposed crystal plane 706. In one embodiment, the crystal
orientation of first exposed crystal plane 704 is different from
the crystal orientation of second exposed crystal plane 706. In a
specific embodiment, substrate 700 is composed of silicon, first
exposed crystal plane 704 has <100> orientation, and second
exposed crystal plane 706 has <110> orientation.
Substrate 700 may be subjected to a radical oxidation process to
form a dielectric layer by consuming (oxidizing) the top surface of
substrate 700. In one embodiment, the oxidizing of substrate 700 by
a radical oxidation process includes oxidizing with a radical
selected from the group consisting of an OH radical, an HO.sub.2
radical or an O diradical. FIG. 7B illustrates a cross-sectional
view of substrate 700 including first and second crystal planes 704
and 706, respectively, and having a dielectric layer 708 formed
thereon, in accordance with an embodiment of the present invention.
In an embodiment, first portion 708A of dielectric layer 708 is
formed on first exposed crystal plane 704 and a second portion 708B
of dielectric layer 708 is formed on second exposed crystal plane
706, as depicted in FIG. 7B. In one embodiment, the thickness T1 of
first portion 708A of dielectric layer 708 is approximately equal
to the thickness T2 of second portion 708B of dielectric layer 708,
even though the crystal plane orientation of first exposed crystal
plane 704 and second exposed crystal plane 706 differ. In a
specific embodiment, the radical oxidation of substrate 700 is
carried out at a temperature approximately in the range of 600-900
degrees Celsius. In a specific embodiment, the radical oxidation of
substrate 700 is carried out at a temperature approximately in the
range of 700-800 degrees Celsius at a pressure approximately in the
range of 0.5-5 Torr.
Thus, a method for fabricating a nonvolatile charge trap memory
device has been disclosed. In accordance with an embodiment of the
present invention, a substrate is provided having a charge-trapping
layer disposed thereon. A portion of the charge-trapping layer is
then oxidized to form a blocking dielectric layer above the
charge-trapping layer by exposing the charge-trapping layer to a
radical oxidation process.
In another aspect of the present invention, it may be desirable to
use a cluster tool to carry out a radical oxidation process.
Accordingly, disclosed herein is a method to fabricate a
nonvolatile charge trap memory device. A substrate may first be
subjected to a first radical oxidation process to form a first
dielectric layer in a first process chamber of a cluster tool. In
one embodiment, a charge-trapping layer is then deposited above the
first dielectric layer in a second process chamber of the cluster
tool. The charge-trapping layer may then be subjected to a second
radical oxidation process to form a second dielectric layer above
the charge-trapping layer. In one embodiment, the second dielectric
layer is formed by oxidizing a portion of the charge-trapping layer
in the first process chamber of the cluster tool. In a specific
embodiment, the cluster tool is a single-wafer cluster tool.
Formation of a dielectric layer in a chamber of a cluster tool may
permit the growth of the dielectric layer at temperatures higher
than normally achievable in batch processing chambers. Furthermore,
a radical oxidation process may be carried out in the chamber of
the cluster tool as the primary pathway for growing the dielectric
layer. In accordance with an embodiment of the present invention, a
radical oxidation process involving flowing hydrogen (H.sub.2) and
oxygen (O.sub.2) gas into an oxidation chamber of a cluster tool is
carried out to effect growth of a dielectric layer by oxidation
consumption of an exposed substrate or film. In one embodiment,
multiple radical oxidation processes are carried out in an
oxidation chamber of a cluster tool to provide a tunnel dielectric
layer and a blocking dielectric layer for a non-volatile charge
trap memory device. These dielectric layers may be of very high
quality, even at a reduced thickness. In one embodiment, the tunnel
dielectric layer and the blocking dielectric layer are both denser
and are composed of substantially fewer hydrogen atoms/cm.sup.3
than a tunnel dielectric layer or a blocking dielectric layer
formed in a batch process chamber. Furthermore, the substrate upon
which a tunnel dielectric layer and a blocking dielectric layer are
formed may be exposed to a shorter temperature ramp rate and
stabilization time in an oxidation chamber of a cluster tool as
compared with a batch process chamber. Thus, in accordance with an
embodiment of the present invention embodiment, the impact on the
thermal budget of the substrate is reduced by employing a radical
oxidation process in an oxidation chamber of a cluster tool. In
accordance with another embodiment of the present invention, a
dielectric layer formed by carrying out a radical oxidation process
in an oxidation chamber of a cluster tool is less susceptible to
crystal plane orientation differences in the substrate from which
it is grown. In one embodiment, the cornering effect caused by
differential crystal plane oxidation rates is significantly reduced
by forming a dielectric layer via a radical oxidation process
carried out in an oxidation chamber of a cluster tool.
A portion of a nonvolatile charge trap memory device may be
fabricated in a cluster tool. FIG. 8 illustrates an arrangement of
process chambers in a cluster tool, in accordance with an
embodiment of the present invention. Referring to FIG. 8, an
arrangement of process chambers in a cluster tool 800 includes a
transfer chamber 802, a first process chamber 804, a second process
chamber 806 and a third process chamber 808. In an embodiment,
transfer chamber 802 is for receiving a wafer from an external
environment for introduction into cluster tool 800. In one
embodiment, each of the process chambers 802, 804 and 806 are
arranged in a way such that a wafer may be passed back- and forth
between these chambers and transfer chamber 802, as depicted by the
double-headed arrows in FIG. 8. In accordance with an additional
embodiment of the present invention, although not shown, cluster
tool 800 may be configured such that a wafer can be transferred
directly between any pairing of process chambers 802, 804 or
806.
Cluster tool 800 may be any cluster tool for which an outside
environment is excluded in and between process chambers 804, 806
and 808 and transfer chamber 802. Thus, in accordance with an
embodiment of the present invention, once a wafer has entered
process chamber 802, it is protected from an external environment
as it is moved into and between process chambers 804, 806 and 808
and transfer chamber 802. An example of such a cluster tool is the
Centura.RTM. platform commercially available from Applied
Materials, Inc., located in Santa Clara, Calif. In one embodiment,
once a wafer has been received by transfer chamber 802, a vacuum of
less than approximately 100 mTorr is maintained in cluster tool
800. In accordance with an embodiment of the present invention,
cluster tool 800 incorporates a chuck (or multiple chucks, e.g.,
one chuck for each chamber) upon which the flat surface, as opposed
to the edge surface, of a wafer rests on the chuck for processing
and transfer events. In one embodiment, by having the flat surface
of a wafer rest on the chuck, more rapid ramp rates for heating the
wafer are achievable by heating the wafer via the chuck. In a
specific embodiment, cluster tool 800 is a single-wafer cluster
tool.
Process chambers 802, 804 and 806 may include, but are not limited
to, oxidation chambers, low-pressure chemical vapor deposition
chambers, or a combination thereof. For example, in accordance with
an embodiment of the present invention, first process chamber 804
is a first oxidation chamber, second process chamber 806 is a
low-pressure chemical vapor deposition chamber, and third process
chamber 808 is a second oxidation chamber. An example of an
oxidation chamber is the In-Situ Steam Generation (ISSG) chamber
from Applied Materials, Inc. Examples of low-pressure chemical
vapor deposition chambers include a SiNgen.TM. chamber and an
OXYgen.TM. chamber from Applied Materials, Inc. Instead of heating
entire process chambers to heat a wafer, which is the case for
typical batch process chambers, a chuck used for carrying a single
wafer may be heated to heat the wafer. In accordance with an
embodiment of the present invention, a chuck is used to heat a
wafer to the desired process temperature. Thus, relatively short
temperature ramp times and stabilization times may be achieved.
A portion of a nonvolatile charge trap memory device may be
fabricated in a cluster tool. FIG. 9 depicts a Flowchart 900
representing a series of operations in a method for fabricating a
nonvolatile charge trap memory device, in accordance with an
embodiment of the present invention. FIGS. 10A-10E illustrate
cross-sectional views representing operations in the fabrication of
a nonvolatile charge trap memory device, in accordance with an
embodiment of the present invention.
Referring to FIG. 10A, a substrate 1000 is provided in a cluster
tool. In one embodiment, substrate 1000 is provided in a transfer
chamber, such as transfer chamber 802 described in association with
FIG. 8.
Substrate 1000 may be composed of any material suitable for
semiconductor device fabrication. In one embodiment, substrate 1000
is a bulk substrate composed of a single crystal of a material
which may include, but is not limited to, silicon, germanium,
silicon-germanium or a III-V compound semiconductor material. In
another embodiment, substrate 1000 includes a bulk layer with a top
epitaxial layer. In a specific embodiment, the bulk layer is
composed of a single crystal of a material which may include, but
is not limited to, silicon, germanium, silicon-germanium, a III-V
compound semiconductor material or quartz, while the top epitaxial
layer is composed of a single crystal layer which may include, but
is not limited to, silicon, germanium, silicon-germanium or a III-V
compound semiconductor material. In another embodiment, substrate
1000 includes a top epitaxial layer on a middle insulator layer
which is above a lower bulk layer. The top epitaxial layer is
composed of a single crystal layer which may include, but is not
limited to, silicon (i.e. to form a silicon-on-insulator (SOI)
semiconductor substrate), germanium, silicon-germanium or a III-V
compound semiconductor material. The insulator layer is composed of
a material which may include, but is not limited to, silicon
dioxide, silicon nitride or silicon oxy-nitride. The lower bulk
layer is composed of a single crystal which may include, but is not
limited to, silicon, germanium, silicon-germanium, a III-V compound
semiconductor material or quartz. Substrate 1000 may further
include dopant impurity atoms.
FIG. 10B illustrates a cross-sectional view of a substrate having a
tunnel dielectric layer formed thereon, corresponding to operation
902 from the Flowchart of FIG. 9, in accordance with an embodiment
of the present invention. Referring to operation 902 of Flowchart
900 and corresponding FIG. 10B, substrate 1000 is subjected to a
first radical oxidation process in a first process chamber of the
cluster tool to form a first dielectric layer 1002.
First dielectric layer 1002 may be composed of a material and have
a thickness suitable to allow charge carriers to tunnel into a
subsequently formed charge-trapping layer under an applied gate
bias, while maintaining a suitable barrier to leakage when a
subsequently formed nonvolatile charge trap memory device is
unbiased. In accordance with an embodiment of the present
invention, first dielectric layer 1002 is formed by an oxidation
process where the top surface of substrate 1000 is consumed. Thus,
in an embodiment, first dielectric layer 1002 is composed of an
oxide of the material of substrate 1000. For example, in one
embodiment, substrate 1000 is composed of silicon and first
dielectric layer 1002 is composed of silicon dioxide. In a specific
embodiment, first dielectric layer 1002 is formed to a thickness
approximately in the range of 1-10 nanometers. In a particular
embodiment, first dielectric layer 1002 is formed to a thickness
approximately in the range of 1.5-2.5 nanometers.
First dielectric layer 1002 may be formed by a radical oxidation
process. In accordance with an embodiment of the present invention,
the radical oxidation process involves flowing hydrogen (H.sub.2)
and oxygen (O.sub.2) gas into an oxidation chamber, such as the
oxidation chambers 804 or 808 described in association with FIG. 8.
In one embodiment, the partial pressures of H.sub.2 and O.sub.2
have a ratio to one another approximately in the range of 1:50-1:5.
However, in an embodiment, an ignition event is not carried out
which would otherwise typically be used to pyrolyze the H.sub.2 and
O.sub.2 to form steam. Instead, H.sub.2 and O.sub.2 are permitted
to react to form radicals at the surface of substrate 1000. In one
embodiment, the radicals are used to consume the top portion of
substrate 1000 to provide first dielectric layer 1002. In a
specific embodiment, the radical oxidation process includes
oxidizing with a radical such as, but not limited to, an OH
radical, an HO.sub.2 radical or an O diradical. In a particular
embodiment, the radical oxidation process is carried out at a
temperature approximately in the range of 950-1100 degrees Celsius
at a pressure approximately in the range of 5-15 Torr. In one
embodiment, the radical oxidation process is carried out for a
duration approximately in the range of 1-3 minutes. In accordance
with an embodiment of the present invention, first dielectric layer
1002 is formed as a high-density, low-hydrogen-content film.
Referring to operation 904 of Flowchart 900, subsequent to forming
first dielectric layer 1002, but prior to any further processing,
first dielectric layer 1002 may be subjected to a nitridation
process. In an embodiment, the nitridation process is carried out
in the same process chamber used to form first dielectric layer
1002. In one embodiment, first dielectric layer 1002 is annealed in
the first process chamber, wherein the annealing includes heating
substrate 1000 in an atmosphere including nitrogen at a temperature
approximately in the range of 900-1100 degrees Celsius for a
duration approximately in the range of 30 seconds-60 seconds. In
one embodiment, the atmosphere including nitrogen is composed of a
gas such as, but not limited to, nitrogen (N.sub.2), nitrous oxide
(N.sub.2O), nitrogen dioxide (NO.sub.2), nitric oxide (NO) or
ammonia (NH.sub.3). In another embodiment, the nitridation occurs
in a separate process chamber. Alternatively, this nitridation step
may be skipped.
FIG. 10C illustrates a cross-sectional view of a substrate having a
charge-trapping layer formed thereon, corresponding to operation
906 from the Flowchart of FIG. 9, in accordance with an embodiment
of the present invention. Referring to operation 906 of Flowchart
900 and corresponding FIG. 10C, a charge-trapping layer having a
first region 1004A and a second region 1004B is formed on first
dielectric layer 1002 in the second process chamber of a cluster
tool.
The charge-trapping layer may be composed of a material and have a
thickness suitable to store charge and, hence, change the threshold
voltage of a subsequently formed gate stack. In accordance with an
embodiment of the present invention, the charge-trapping layer is
composed of two regions 1004A and 1004B, as depicted in FIG. 10C.
In an embodiment, region 1004A of the charge-trapping layer will
remain as an intact charge-trapping layer following subsequent
process operations. However, in that embodiment, region 1004B of
the as-formed charge-trapping layer will be consumed to form a
second dielectric layer, above region 1004A. In one embodiment,
regions 1004A and 1004B of the charge-trapping layer are formed in
the same process step and are composed of the same material.
The charge-trapping layer having regions 1004A and 1004B may be
formed by a chemical vapor deposition process. In accordance with
an embodiment of the present invention, the charge-trapping layer
is composed of a material such as, but not limited to, silicon
nitride, silicon oxy-nitride, oxygen-rich silicon oxy-nitride or
silicon-rich silicon oxy-nitride. In an embodiment, the
charge-trapping layer is formed on first dielectric layer 1002 in a
low-pressure chemical vapor deposition chamber, such as the
SiNgen.TM. low-pressure chemical vapor deposition chamber described
in association with process chamber 806 from FIG. 8. In one
embodiment, the second process chamber is a low-pressure chemical
vapor deposition chamber and regions 1004A and 1004B of the
charge-trapping layer are formed at a temperature less than the
temperature used to form first dielectric layer 1002. In a specific
embodiment, regions 1004A and 1004B of the charge-trapping layer
are formed at a temperature approximately in the range of 700-850
degrees Celsius. In an embodiment, the second process chamber is a
low-pressure chemical vapor deposition chamber and the
charge-trapping layer is formed by using gases such as, but not
limited to, dichlorosilane (H.sub.2SiCl.sub.2),
bis-(tert-butylamino)silane (BTBAS), ammonia (NH.sub.3) or nitrous
oxide (N.sub.2O). In accordance with an embodiment of the present
invention, the charge-trapping layer is formed to a total thickness
approximately in the range of 5-15 nanometers and region 1004B
accounts for a thickness approximately in the range of 2-3
nanometers of the total thickness of the charge-trapping layer. In
that embodiment, region 1004A accounts for the remaining total
thickness of the charge-trapping layer, i.e. the portion of the
charge-trapping layer that is not subsequently consumed to form a
top or blocking dielectric layer.
In another aspect of the present invention, the charge-trapping
layer may include multiple composition regions. For example, in
accordance with an embodiment of the present invention, the
charge-trapping layer includes an oxygen-rich portion and a
silicon-rich portion and is formed by depositing an oxygen-rich
oxy-nitride film by a first composition of gases in the second
process chamber and, subsequently, depositing a silicon-rich
oxy-nitride film by a second composition of gases in the second
process chamber. In one embodiment, the charge-trapping layer is
formed by modifying the flow rate of ammonia (NH.sub.3) gas, and
introducing nitrous oxide (N.sub.2O) and dichlorosilane
(SiH.sub.2Cl.sub.2) to provide the desired gas ratios to yield
first an oxygen-rich oxy-nitride film and then a silicon-rich
oxy-nitride film. In a specific embodiment, the oxygen-rich
oxy-nitride film is formed by introducing a process gas mixture
including N.sub.2O, NH.sub.3 and SiH.sub.2Cl.sub.2, while
maintaining the chamber at a pressure approximately in the range of
0.5-500 Torr, and maintaining substrate 1000 at a temperature
approximately in the range of 700-850 degrees Celsius, for a period
approximately in the range of 2.5-20 minutes. In a further
embodiment, the process gas mixture includes N.sub.2O and NH.sub.3
having a ratio of from about 8:1 to about 1:8 and SiH.sub.2Cl.sub.2
and NH.sub.3 having a ratio of from about 1:7 to about 7:1, and can
be introduced at a flow rate approximately in the range of 5-200
standard cubic centimeters per minute (sccm). In another specific
embodiment, the silicon-rich oxy-nitride film is formed by
introducing a process gas mixture including N.sub.2O, NH.sub.3 and
SiH.sub.2Cl.sub.2, while maintaining the chamber at a pressure
approximately in the range of 0.5-500 Torr, and maintaining
substrate 1000 at a temperature approximately in the range of
700-850 degrees Celsius, for a period approximately in the range of
2.5-20 minutes. In a further embodiment, the process gas mixture
includes N.sub.2O and NH.sub.3 having a ratio of from about 8:1 to
about 1:8 and SiH.sub.2Cl.sub.2 and NH.sub.3 mixed in a ratio of
from about 1:7 to about 7:1, introduced at a flow rate of from
about 5 to about 20 sccm. In accordance with an embodiment of the
present invention, the charge-trapping layer comprises a bottom
oxygen-rich silicon oxy-nitride portion having a thickness
approximately in the range of 2.5-3.5 nanometers and a top
silicon-rich silicon oxy-nitride portion having a thickness
approximately in the range of 9-10 nanometers. In one embodiment, a
region 1004B of charge-trapping layer accounts for a thickness
approximately in the range of 2-3 nanometers of the total thickness
of the top silicon-rich silicon oxy-nitride portion of the
charge-trapping layer. Thus, region 1004B, which is targeted for
subsequent consumption to form a second dielectric layer, may be
composed entirely of silicon-rich silicon oxy-nitride.
FIG. 10D illustrates a cross-sectional view of a substrate having a
top dielectric layer formed thereon, corresponding to operation 908
from the Flowchart of FIG. 9, in accordance with an embodiment of
the present invention. Referring to operation 908 of Flowchart 900
and corresponding FIG. 10D, a second dielectric layer 1006 is
formed on charge-trapping layer 1004 in the first process chamber
of the cluster tool.
Second dielectric layer 1006 may be composed of a material and have
a thickness suitable to maintain a barrier to charge leakage
without significantly decreasing the capacitance of a subsequently
formed gate stack in a nonvolatile charge trap memory device. In
accordance with an embodiment of the present invention, second
dielectric layer 1006 is formed by consuming region 1004B of the
charge trapping layer formed in operation 906, described in
association with FIG. 10C. Thus, in one embodiment region 1004B is
consumed to provide second dielectric layer 1006, while region
1004A remains a charge-trapping layer 1004. In a specific
embodiment, region 1004B is a silicon-rich silicon oxy-nitride
region having a thickness approximately in the range of 2-3
nanometers and is oxidized to form second dielectric layer 1006
having a thickness approximately in the range of 3.5-4.5
nanometers. In that embodiment, second dielectric layer 1006 is
composed of silicon dioxide.
Second dielectric layer 1006 may be formed by a second radical
oxidation process. In accordance with an embodiment of the present
invention, the second radical oxidation process involves flowing
hydrogen (H.sub.2) and oxygen (O.sub.2) gas into an oxidation
chamber, such as the oxidation chambers 804 or 808 described in
association with FIG. 8. In one embodiment, the partial pressures
of H.sub.2 and O.sub.2 have a ratio to one another approximately in
the range of 1:50-1:5. However, in an embodiment, an ignition event
is not carried out which would otherwise typically be used to
pyrolyze the H.sub.2 and O.sub.2 to form steam. Instead, H.sub.2
and O.sub.2 are permitted to react to form radicals at the surface
of region 1004B. In one embodiment, the radicals are used to
consume region 1004B to provide second dielectric layer 1006. In a
specific embodiment, the second radical oxidation process includes
oxidizing with a radical such as, but not limited to, an OH
radical, an HO.sub.2 radical or an O diradical. In a particular
embodiment, the second radical oxidation process is carried out at
a temperature approximately in the range of 950-1100 degrees
Celsius at a pressure approximately in the range of 5-15 Torr. In
one embodiment, the second radical oxidation process is carried out
for a duration approximately in the range of 1-3 minutes. In
accordance with an embodiment of the present invention, first
dielectric layer 1002 is formed as a high-density,
low-hydrogen-content film. In one embodiment, no additional
deposition step is required to form a complete second dielectric
layer 1006, as depicted in FIG. 10D and shown in Flowchart 900.
Depending on wafer pass-through logistics in the cluster tool, the
second radical oxidation process may be carried out in the same,
i.e. first, chamber as the first radical oxidation process used to
form first dielectric layer 1002 or in a different, e.g. third,
process chamber of the cluster tool. Thus, in accordance with an
embodiment of the present invention, reference to a first process
chamber can be used to mean reintroduction into the first process
chamber or to mean introduction into a process chamber different
from the first process chamber.
Referring to operation 910 of Flowchart 900, subsequent to forming
second dielectric layer 1006, but prior to removing substrate 1000
from the cluster tool, second dielectric layer 1006 may be further
subjected to a nitridation process in the first process chamber. In
accordance with an embodiment of the present invention, the
nitridation process includes annealing second dielectric layer 1006
in an atmosphere including nitrogen at a temperature approximately
in the range of 900-1100 degrees Celsius for a duration
approximately in the range of 30 seconds-60 seconds. In one
embodiment, the atmosphere including nitrogen is composed of a gas
such as, but not limited to, nitrogen (N.sub.2), nitrous oxide
(N.sub.2O), nitrogen dioxide (NO.sub.2), nitric oxide (NO) or
ammonia (NH.sub.3). Alternatively, this nitridation step, i.e.
operation 910 from Flowchart 900, may be skipped and the wafer
unloaded from the cluster tool.
Thus, in accordance with an embodiment of the present invention, an
ONO stack including first dielectric layer 1002, charge-trapping
layer 1004 and second dielectric layer 1006 is formed in a single
pass in a cluster tool. By fabricating these layers in a single
pass in the cluster tool, pristine interfaces between first
dielectric layer 1002 and charge-trapping layer 1004 and between
charge-trapping layer 1004 and second dielectric layer 1006 may be
preserved. In one embodiment, first dielectric layer 1002,
charge-trapping layer 1004 and second dielectric layer 1006 are
formed without breaking vacuum in the cluster tool. In one
embodiment, each layer is formed at a different temperature to
tailor film properties without incurring significant ramp time
penalties. Furthermore, by fabricating these layers in a cluster
tool, as opposed to fabricating in batch processing tools, the
overall uniformity of the stack of layers may be optimized. For
example, in accordance with an embodiment of the present invention,
by fabricating layers 1002, 1004 and 1006 in a cluster tool, the
variability in thickness of the stack of layers 1002, 1004 and 1006
across a single wafer may be reduced by as much as approximately
30%. In an exemplary embodiment, 1 .sigma. is approximately in the
range of 1-2% of the thickness of first dielectric layer 1002. In a
specific embodiment, the cluster tool is a single-wafer cluster
tool.
Upon fabrication of an ONO stack including first dielectric layer
1002, charge-trapping layer 1004 and second dielectric layer 1006,
a nonvolatile charge trap memory device may be fabricated to
include a patterned portion of the ONO stack. FIG. 10E illustrates
a cross-sectional view of a nonvolatile charge trap memory device,
in accordance with an embodiment of the present invention.
Referring to FIG. 10E, a nonvolatile charge trap memory device
includes a patterned portion of the ONO stack formed over substrate
1000. The ONO stack includes first dielectric layer 1002,
charge-trapping layer 1004 and second dielectric layer 1006. A gate
layer 1008 is disposed on second dielectric layer 1006. The
nonvolatile charge trap memory device further includes source and
drain regions 1012 in substrate 1000 on either side of the ONO
stack, defining a channel region 1014 in substrate 1000 underneath
the ONO stack. A pair of dielectric spacers 1010 isolates the
sidewalls of first dielectric layer 1002, charge-trapping layer
1004, second dielectric layer 1006 and gate layer 1008. In a
specific embodiment, channel region 1014 is doped P-type and, in an
alternative embodiment, channel region 1014 is doped N-type.
In accordance with an embodiment of the present invention, the
nonvolatile charge trap memory device described in association with
FIG. 10E is a SONOS-type device. By convention, SONOS stands for
"Semiconductor-Oxide-Nitride-Oxide -Semiconductor," where the first
"Semiconductor" refers to the channel region material, the first
"Oxide" refers to the tunnel dielectric layer, "Nitride" refers to
the charge-trapping dielectric layer, the second "Oxide" refers to
the top dielectric layer (also known as a blocking dielectric
layer) and the second "Semiconductor" refers to the gate layer.
Thus, in accordance with an embodiment of the present invention,
first dielectric layer 1002 is a tunnel dielectric layer and second
dielectric layer 1006 is a blocking dielectric layer.
Gate layer 1008 may be composed of any conductor or semiconductor
material suitable for accommodating a bias during operation of a
SONOS-type transistor. In accordance with an embodiment of the
present invention, gate layer 1008 is formed by a chemical vapor
deposition process and is composed of doped poly-crystalline
silicon. In another embodiment, gate layer 1008 is formed by
physical vapor deposition and is composed of a metal-containing
material which may include, but is not limited to, metal nitrides,
metal carbides, metal silicides, hafnium, zirconium, titanium,
tantalum, aluminum, ruthenium, palladium, platinum, cobalt or
nickel.
Source and drain regions 1012 in substrate 1000 may be any regions
having opposite conductivity to channel region 1014. For example,
in accordance with an embodiment of the present invention, source
and drain regions 1012 are N-type doped regions while channel
region 1014 is a P-type doped region. In one embodiment, substrate
1000 and, hence, channel region 1014, is composed of boron-doped
single-crystal silicon having a boron concentration in the range of
1.times.10.sup.15-1.times.10.sup.19 atoms/cm.sup.3. In that
embodiment, source and drain regions 1012 are composed of
phosphorous- or arsenic-doped regions having a concentration of
N-type dopants in the range of 5.times.10.sup.16-5.times.10.sup.19
atoms/cm.sup.3. In a specific embodiment, source and drain regions
1012 have a depth in substrate 1000 in the range of 80-200
nanometers. In accordance with an alternative embodiment of the
present invention, source and drain regions 1012 are P-type doped
regions while channel region 1014 is an N-type doped region.
In another aspect of the present invention, a charge-trapping layer
may include multiple composition regions, where the composition
region closest to a tunnel dielectric layer is subjected to a
radical oxidation process. FIG. 11 depicts a Flowchart 1100
representing a series of operations in a method for fabricating a
nonvolatile charge trap memory device, in accordance with an
embodiment of the present invention. FIGS. 12A-12E illustrate
cross-sectional views representing operations in the fabrication of
a nonvolatile charge trap memory device, in accordance with an
embodiment of the present invention.
FIG. 12A illustrates a cross-sectional view of a substrate having a
first dielectric layer formed thereon, corresponding to operation
1102 from the Flowchart of FIG. 11, in accordance with an
embodiment of the present invention. Referring to operation 1102 of
Flowchart 1100 and corresponding FIG. 12A, substrate 1200 is
subjected to a first radical oxidation process in a first process
chamber of a cluster tool to form a first dielectric layer 1202.
Substrate 1200 and first dielectric layer 1202 may be composed of
materials described in association with substrate 1000 and first
dielectric layer 1002 from FIGS. 10A and 10B, respectively. The
radical oxidation process used to form first dielectric layer 1202
may be similar to the radical oxidation process used to form first
dielectric layer 1002, described in association with FIG. 10B.
Referring to operation 1104 of Flowchart 1100, subsequent to
forming first dielectric layer 1202, but prior to any further
processing, first dielectric layer 1202 may be subjected to a
nitridation process. The nitridation process may be similar to the
nitridation process described in association with operation 904 of
Flowchart 900. In one embodiment, the nitridation process is
carried out in the same process chamber used to form first
dielectric layer 1202. In another embodiment, the nitridation
occurs in a separate process chamber. Alternatively, this
nitridation step may be skipped.
FIG. 12B illustrates a cross-sectional view of a substrate having
an oxygen-rich silicon oxy-nitride portion of a charge-trapping
layer formed thereon, corresponding to operation 1106 from the
Flowchart of FIG. 11, in accordance with an embodiment of the
present invention. Referring to operation 1106 of Flowchart 1100
and corresponding FIG. 12B, an oxygen-rich silicon oxy-nitride
portion 1204A is formed on first dielectric layer 1202 in a second
process chamber of the cluster tool. Oxygen-rich silicon
oxy-nitride portion 1204A may be composed of an oxygen-rich silicon
oxy-nitride material and formed by a technique described in
association with first region 1004A from FIG. 10C.
Referring to operation 1108 from Flowchart 1100, in accordance with
an embodiment of the present invention, oxygen-rich silicon
oxy-nitride portion 1204A is subjected to a second radical
oxidation process in the first process chamber of the cluster tool.
The second radical oxidation process may be similar to one of the
radical oxidation processes used to form first dielectric layer
1002 or second dielectric layer 1006, described in association with
FIGS. 10B and 10D, respectively. In an embodiment, carrying out the
second radical oxidation process is made possible because
oxygen-rich silicon oxy-nitride portion 1204A is maintained in the
environment within the tool and thus retains a pristine surface. In
one embodiment, the second radical oxidation process densifies
oxygen-rich silicon oxy-nitride portion 1204A. Depending on wafer
pass-through logistics in the cluster tool, the second radical
oxidation process may be carried out in the same, i.e. first,
chamber as the radical oxidation process used to form first
dielectric layer 1202 or in a different, e.g. third, process
chamber. Thus, in accordance with an embodiment of the present
invention, reference to a first process chamber can be used to mean
reintroduction into the first process chamber or to mean
introduction into a process chamber different from the first
process chamber.
FIG. 12C illustrates a cross-sectional view of a substrate having a
silicon-rich silicon oxy-nitride portion of a charge-trapping layer
formed thereon, corresponding to operation 1110 from the Flowchart
of FIG. 11, in accordance with an embodiment of the present
invention. Referring to operation 1110 of Flowchart 1100 and
corresponding FIG. 12C, a silicon-rich silicon oxy-nitride portion
having a first region 1204B and a second region 1204C is formed on
oxygen-rich silicon oxy-nitride portion 1204A in the second process
chamber of the cluster tool. The silicon-rich silicon oxy-nitride
portion may be composed of a silicon-rich silicon oxy-nitride
material and formed by a technique described in association with
second region 1004B from FIG. 10C. Depending on wafer pass-through
logistics in the cluster tool, the deposition of silicon-rich
silicon oxy-nitride portion of the charge-trapping layer may be
carried out in the same, i.e. second, chamber as the deposition of
oxygen-rich silicon oxy-nitride portion 1204A of the
charge-trapping layer or in a different process chamber. Thus, in
accordance with an embodiment of the present invention, reference
to a second process chamber can be used to mean reintroduction into
the second process chamber or to mean introduction into a process
chamber different from the second process chamber.
FIG. 12D illustrates a cross-sectional view of a substrate having a
top dielectric layer formed thereon, corresponding to operation
1112 from the Flowchart of FIG. 11, in accordance with an
embodiment of the present invention. Referring to operation 1112 of
Flowchart 1100 and corresponding FIG. 12D, a second dielectric
layer 1206 is formed on charge-trapping layer 1204 in the first
process chamber of the cluster tool. In accordance with an
embodiment of the present invention, second dielectric layer 1206
is formed by consuming second region 1204C of the silicon-rich
silicon oxy-nitride portion by a third radical oxidation process.
Thus, in one embodiment, the remaining charge-trapping layer 1204
between first dielectric layer 1202 and second dielectric layer
1204 is composed of oxygen-rich silicon oxy-nitride portion 1204A
and first region 1204B of the silicon-rich silicon oxy-nitride
portion 1204, as depicted in FIG. 12D. The third radical oxidation
process used to consume second region 1204C of the silicon-rich
silicon oxy-nitride portion to provide second dielectric layer 1206
may be similar to the radical oxidation process used to form second
dielectric layer 1006, described in association with FIG. 10D.
Depending on wafer pass-through logistics in the cluster tool, the
third radical oxidation process may be carried out in the same,
i.e. first, chamber as the radical oxidation process used to form
first dielectric layer 1202 or in a different, e.g. third, process
chamber. Thus, in accordance with an embodiment of the present
invention, reference to a first process chamber can be used to mean
reintroduction into the first process chamber or to mean
introduction into a process chamber different from the first
process chamber.
Referring to operation 1114 of Flowchart 1100, subsequent to
forming second dielectric layer 1206, but prior to removing
substrate 1200 from the cluster tool, second dielectric layer 1206
may be further subjected to a nitridation process in the first
process chamber. The nitridation process may be similar to the
nitridation process described in association with operation 910
from Flowchart 900. In one embodiment, the nitridation process is
carried out in the same process chamber used to form second
dielectric layer 1206. In another embodiment, the nitridation
occurs in a separate process chamber. Alternatively, this
nitridation step may be skipped.
Upon fabrication of an ONO stack including first dielectric layer
1202, charge-trapping layer 1204 and second dielectric layer 1206,
a nonvolatile charge trap memory device may be fabricated to
include a patterned portion of the ONO stack. FIG. 12E illustrates
a cross-sectional view of a nonvolatile charge trap memory device,
in accordance with an embodiment of the present invention.
Referring to FIG. 12E, a nonvolatile charge trap memory device
includes a patterned portion of the ONO stack formed over substrate
1200. The ONO stack includes first dielectric layer 1202,
charge-trapping layer 1204 and second dielectric layer 1206. A gate
layer 1208 is disposed on second dielectric layer 1206. The
nonvolatile charge trap memory device further includes source and
drain regions 1212 in substrate 1200 on either side of the ONO
stack, defining a channel region 1214 in substrate 1200 underneath
the ONO stack. A pair of dielectric spacers 1210 isolates the
sidewalls of first dielectric layer 1202, charge-trapping layer
1204, second dielectric layer 1206 and gate layer 1208. In
accordance with an embodiment of the present invention,
charge-trapping layer 1204 is composed of an oxygen-rich silicon
oxy-nitride portion 1204A and a silicon-rich silicon oxy-nitride
portion 1204B, as depicted in FIG. 12E. In one embodiment, the
nonvolatile charge trap memory device is a SONOS-type device. Gate
layer 1208, source and drain regions 1212 and channel region 1214
may be composed of materials described in association with gate
layer 1008, source and drain regions 1012 and channel region 1014
from FIG. 10E.
In another aspect of the present invention, a dielectric layer
formed by radical oxidation of the top surface of a substrate in an
oxidation chamber may be less susceptible to crystal plane
orientation differences in the substrate upon which it is grown.
For example, in one embodiment, the cornering effect caused by
differential crystal plane oxidation rates is significantly reduced
by forming a dielectric layer in an oxidation chamber of a cluster
tool. FIG. 13A illustrates a cross-sectional view of a substrate
including first and second exposed crystal planes, in accordance
with an embodiment of the present invention.
Referring to FIG. 13A, a substrate 1300 has isolation regions 1302
formed thereon. Substrate 1300 may be composed of a material
described in association with substrate 1000 from FIG. 10A.
Isolation regions 1302 may be composed of an insulating material
suitable for adhesion to substrate 1300. An exposed portion of
substrate 1300 extends above the top surface of isolation regions
1302. In accordance with an embodiment of the present invention,
the exposed portion of substrate 1300 has a first exposed crystal
plane 1304 and a second exposed crystal plane 1306. In one
embodiment, the crystal orientation of first exposed crystal plane
1304 is different from the crystal orientation of second exposed
crystal plane 1306. In a specific embodiment, substrate 1300 is
composed of silicon, first exposed crystal plane 1304 has
<100>orientation, and second exposed crystal plane 1306 has
<110> orientation.
Substrate 1300 may be subjected to a radical oxidation process in a
cluster tool to form a dielectric layer by consuming (oxidizing)
the top surface of substrate 1300. In one embodiment, the oxidizing
of substrate 1300 by a radical oxidation process includes oxidizing
with a radical selected from the group consisting of an OH radical,
an HO.sub.2 radical or an O diradical. FIG. 13B illustrates a
cross-sectional view of substrate 1300 including first and second
crystal planes 1304 and 1306, respectively, and having a dielectric
layer 1308 formed thereon, in accordance with an embodiment of the
present invention. In an embodiment, first portion 1308A of
dielectric layer 1308 is formed on first exposed crystal plane 1304
and a second portion 1308B of dielectric layer 1308 is formed on
second exposed crystal plane 1306, as depicted in FIG. 13B. In one
embodiment, the thickness T1 of first portion 1308A of dielectric
layer 1308 is approximately equal to the thickness T2 of second
portion 1308B of dielectric layer 1308, even though the crystal
plane orientation of first exposed crystal plane 1304 and second
exposed crystal plane 1306 differ. In a specific embodiment, the
radical oxidation of substrate 1300 is carried out at a temperature
approximately in the range of 950-1100 degrees Celsius at a
pressure approximately in the range of 5-15 Torr. In one
embodiment, subsequent to forming dielectric layer 1308, substrate
1300 is annealed in the oxidation chamber in an atmosphere
including nitrogen at a temperature approximately in the range of
900-1100 degrees Celsius for a duration approximately in the range
of 30 seconds-60 seconds.
Thus, a method for fabricating a nonvolatile charge trap memory
device has been disclosed. In accordance with an embodiment of the
present invention, a substrate is subjected to a first radical
oxidation process to form a first dielectric layer in a first
process chamber of a cluster tool. A charge-trapping layer may then
be deposited above the first dielectric layer in a second process
chamber of the cluster tool. In one embodiment, the charge-trapping
layer is then subjected to a second radical oxidation process to
form a second dielectric layer above the charge-trapping layer by
oxidizing a portion of the charge-trapping layer in the first
process chamber of the cluster tool. By forming all layers of an
oxide-nitride-oxide (ONO) stack in a cluster tool, interface damage
may be reduced between the respective layers. Thus, in accordance
with an embodiment of the present invention, an ONO stack is
fabricated in a single pass in a cluster tool in order to preserve
a pristine interface between the layers in the ONO stack. In a
specific embodiment, the cluster tool is a single-wafer cluster
tool.
* * * * *